The disclosure of Japanese Patent Application No. 2001-131357 filed on Apr. 27, 2001, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to method and apparatus for speed shift control of an automatic transmission installed together with an engine in a vehicle. More particularly, the invention relates to a learning control of a speed shift point in a power-on upshift and, particularly, an upshift in response to a demand for maximum engine output (a fully open throttle state).
2. Description of the Related Art
Generally in an automatic transmission, a speed shift determination is output based on a map (speed shift diagram) pre-determined for vehicle speed versus engine output demand (generally, the degree of throttle opening). With regard to a speed shift during a fully open throttle state where the maximum engine output is requested, it is desirable that the engine rotational speed be equal to an allowable maximum rotational speed. In some cases, however, the engine rotational speed does not reach the allowable maximum rotational speed, or exceeds the allowable maximum rotational speed (generally termed over-revolution), due to variations between individual engines and automatic transmissions introduced in manufacture, engine torque reduction due to deterioration of the engine with age, the engine intake temperature, the intake pressure, etc.
A conventional countermeasure against the aforementioned problem is disclosed in Japanese Patent Publication No. HEI 7-23745. According to that disclosure, a maximum value of the engine rotational speed during a speed shift is detected, and the shift point is changed and corrected so that the maximum engine rotational speed reaches a pre-set reference value. Japanese Patent Publication No. HEI 7-23745 teaches that the engine rotational speed is calculated by multiplying a detected value of the rotational speed of the output shaft of the automatic transmission by the gear ratio (see claim 5). This prior disclosed control method is merely one example of an engine rotational speed detecting method in which the engine rotational speed is not directly detected, and which attempts to determine a maximum engine rotational speed.
However, in the case of what is generally termed a clutch-to-clutch shift, in which a predetermined speed stage is achieved by engaging one friction engagement element while disengaging another friction engagement element, if the engagement timing of the engaging-side friction engagement element is delayed relative to the release timing of the releasing-side friction engagement element, there occurs a state where both of the friction engagement elements are released, and therefore the engine races. If, in such a case, the shift point is corrected by the maximum engine rotational speed, the racing engine rotational speed is used as a reference to correct the shift point.
As indicated in FIGS. 7(a) to 7(c), when the throttle is opened for an upshift (power-on upshift), a shift determination command Us1 is output at a shift point Mp1 in a map based on the vehicle speed (No) and the degree of throttle opening. However, due to the time required for piston stroke of a hydraulic servo and the like, the actual speed shift performed by the switch of engagement of the friction engagement elements is delayed, and therefore the engine rotational speed Ne1 continues to rise. In response to the actual upshift, the engine rotational speed drops so as to correspond to the gear ratio of the post-shift speed stage. After that, the engine rotational speed increases in accordance with the degree of throttle opening.
If the maximum engine rotational speed Nemax is within a pre-set range of target engine rotational speed (set range) NeKxc2x1xcex2 as indicated in FIG. 7(a), the shift point Mp1 is not corrected, i.e., it is maintained as is. If the maximum engine rotational speed Ne1max is higher than the target engine rotational speed NeKxc2x1xcex2 as indicated in FIG. 7(b), it is considered that the engine speed may reach or exceed an allowable rotational speed (generally termed red zone), and therefore the learning correction is performed in such a direction as to advance the timing of the shift point (Mp1xe2x86x92Mp2). As a result, at the time of the next speed shift, a shift determination command Us2 is output based on the learning-corrected shift point Mp2. Therefore, the actual speed shift by the switch of engagement of the friction engagement elements occurs earlier, so that the maximum rotational speed Ne2max of the engine rotational speed Ne2 after the correction comes within the target range for engine rotational speed NeKxc2x1xcex2, as indicated by a broken line in FIG. 7(b).
If the maximum engine rotational speed Ne1max is below the target engine rotational speed NeKxc2x1xcex2 as indicated in FIG. 7(c), it is determined that the actual engine output is below that corresponding to the fully open throttle, and learning correction is performed in a direction to delay the shift point (Mp1xe2x86x92Mp2). As a result, at the next speed shift, a shift determination command Us2 is output based on the learning-corrected shift point Mp2. Therefore, the actual speed shift by switch of the engagement of friction engagement elements occurs at a retarded timing, so that the maximum rotational speed Ne2max for the engine rotational speed Ne2 after the correction comes within the range for target engine rotational speed NeKxc2x1xcex2, as indicated by a broken line in FIG. 7(c).
In a normal case, a correction is made so that the maximum engine rotational speed reaches a target rotational speed even if the learning-correction of the shift point is performed based on the maximum engine rotational speed, as mentioned above. However, as indicated in FIG. 8, if the engine races, that is, if the engaging timing of a friction engagement element is delayed relative to the release timing of a friction engagement element, so that the engine is in a nearly no-load state, the engine rotational speed Ne3 rises at a sharp angle so that the maximum engine rotational speed Ne3max becomes high above the range of the target engine rotational speed NeKxc2x1xcex2. Then, on the basis of the aforementioned learning-correction (see FIG. 7(b)), it is determined that the actual speed shift is late, and a learning-correction is made in a direction to advance the shift point in timing (Mp1xe2x86x92Mp2) as indicated by a broken line, despite the rise of the engine rotational speed Ne3 caused by the engine racing. As a result, the next speed shift is conducted upon the shift determination command Us2 based on the learning-corrected shift point Mp2. Therefore, the post-correction engine rotational speed Ne2 becomes as shown in FIG. 8 (the dot-dash line), and the maximum rotational speed Ne2max falls below the target engine rotational speed NeKxc2x1xcex2.
Thus, the learning-correction of the shift point based on the maximum value of engine rotational speed may result in a false correction if engine racing occurs. The engine racing occurs randomly depending on the clutch-to-clutch shift timing. Therefore, at the next speed shift at a normal timing, the engine rotational speed may fail to reach an allowable maximum rotational speed, so that the maximum output cannot be produced.
Accordingly, it is an object of the invention to provide a method and apparatus for speed shift control of an automatic transmission, with learning-correction even if the engine should race, by detecting the engine rotational speed occurring at the time of initiation of an actual speed shift.
The present invention provides a control apparatus for control of a speed shift in an automatic transmission which is performed responsive to a predetermined shift condition. The control apparatus includes a speed shift determining means for outputting a speed shift determination responsive to satisfaction of the predetermined speed shift condition. Speed shift executing means executes an actual speed shift based on the output speed shift determination and shift initiation-time engine rotational speed detecting means determines the time at which the actual execution of the speed shift is initiated and further detects the engine rotational speed at the time of the initiation of the speed shift. Learning-correcting means corrects the predetermined speed shift condition by comparing the engine rotational speed at the time of initiation of the speed shift with a target engine rotational speed.
In the preferred embodiments, the shift initiation-time engine rotational speed detecting means compares an input rotational speed of the automatic transmission with a value obtained by multiplying an output rotational speed of the automatic transmission by a gear ratio of a pre-shift speed stage.
The control apparatus may include a shift map of vehicle speed versus engine output demand, with vehicle shift speeds plotted thereon. In embodiments including such a map, the learning-correcting means corrects a vehicle shift speed read from the map in such a direction as to decrease the vehicle shift speed if the engine rotational speed at the time of initiation of the shift speed is greater than the target engine rotational speed. On the other hand, if the engine rotational speed at the time of initiation of the speed shift is less than the target engine rotational speed, the learning-correcting means corrects the vehicle shift speed by increasing same. Preferably, these corrections are made by increasing or reducing, as the case may be, a correction value for the vehicle shift speed, by a predetermined amount each control cycle.
The present invention also provides a method for speed shift control of an automatic transmission in which a speed shift is performed based on a predetermined speed shift condition. The method includes outputting a speed shift command responsive to satisfaction of the predetermined shift speed condition, executing an actual speed shift responsive to the speed shift command and determining the time at which the actual execution of the speed shift is initiated. Further, the method involves detecting the engine rotational speed at the determined time of initiation of the speed shift and correcting the predetermined speed shift condition by comparing the engine rotational speed at the time of initiation of the speed shift with a target engine rotational speed.
The determination of the time at which the actual execution of the speed shift is initiated may be made by comparing the input rotational speed of the automatic transmission with a value obtained by multiplying an output rotational speed of the automatic transmission by the gear ratio of the pre-shift speed range.
Determination of satisfaction of the speed shift condition may be by reference to a shift map of vehicle speed versus engine output demand, with vehicle shift speeds plotted thereon. The vehicle shift speed read from the map may be corrected by decreasing same if it is determined that the engine rotational speed at the time of initiation of the speed shift is greater than the target engine rotational speed. On the other hand, the correction increases the vehicle shift speed if it is determined that the engine rotational speed at the time of initiation of the speed shift is less than the target engine rotational speed. Preferably, the correcting increases or reduces a correction value for the vehicle shift speed by a predetermined amount each control cycle.
One preferred application of the method of the present invention is to an upshift executed responsive to a demand for maximum engine output.